I have no idea why it works but it works :-) Basically a modified version of the to-do list app in the Docker's tutorial that let participants to a party write shoutouts on a shared digital whiteboard.
On this page users can add messages to the whiteboard.
This is the page where users visualise the anonymous messages.
This is an admin page that I use to delete the inappropriate messages.
The code is ready to be deployed on a Heroku virtual machine. My whiteboard is a smart television, while participants can utilize every device connected to the internet to write on the former.